1. Field of the Invention
The present invention relates to a radio frequency module configured in a multilayer circuit board whose base material is a resin having flowability during heating and pressurizing, such as a thermoplastic resin, and more particularly, the present invention relates to a radio frequency module including a component that may be a noise generation source provided inside of the radio frequency module.
2. Description of the Related Art
How to implement components on a circuit board in an electronic device with a high density in order to reduce the size of the electronic device has always been a technical problem. Modularizing components to be mounted on a circuit board is effective to increase the density. In many cases, such module components are of the types that include chip components in a multilayer circuit board.
As described above, when a module component including a chip component such as an IC in a multilayer circuit board is made, e.g., a radio frequency module including an IC having an oscillation circuit is provided, there is a problem in that a peripheral circuit is affected by a radio frequency noise generated by the oscillation circuit. For example, JP 2012-190923 A indicates that a ground conductive body pattern is disposed in proximity to an IC chip in order to suppress the effect of such radio frequency noise.
The use of a thermoplastic resin for a base material layer of a multilayer circuit board is attracting attention in recent years. With this multilayer circuit board, a Cu foil is attached to the surface of the thermoplastic resin base material, and a circuit pattern is formed by etching this Cu foil, and a plurality of base material layers are laminated and thermocompression-bonded, so that the multilayer circuit board is formed. When a component is included inside of this multilayer circuit board, the resin around the component flows during the thermocompression-bonding, and accordingly the component is fixed. As described above, the thermoplastic resin can form the multiplayer circuit board using an easy process.
However, when a multilayer circuit board which includes an IC chip including an oscillation circuit therein is made according to the above production method using a thermoplastic resin for the base material layer, the following problem may occur when a ground conductive body pattern for suppressing noise emission from around the oscillation circuit is disposed in proximity. More specifically, the periphery of the IC chip is a cavity formed in advance, and for this reason, even though it is necessary to flow a large amount of resin into the cavity, the ground conductive body pattern blocks the resin from spreading. As a result, a gap is generated because the resin insufficiently spreads into the cavity, and this may cause failure to fix the IC chip.
FIGS. 9A to 9C are views illustrating an example of such a process. As shown in FIG. 9A, a cavity 4 is formed by a stacked body including base material layers 1c, 1d having an opening formed therein and base material layers 1a, 1b without any opening formed therein, and an IC chip 20 is provided in the cavity 4, and thereafter, as shown in FIG. 9B, a stacked body made of base material layers 1e, 1f is placed thereon. Subsequently, as shown in FIG. 9C, heating and pressurizing are performed. At this occasion, the ground conductive body pattern 2i blocks the resin from spreading, and a gap Vd remains (the gap Vd is formed).